Fans in general operate in environmental conditions which usually permit hours of maintenance-free operation before cleaning is required. This applies also to fans used for removing air-borne particles from the air or dirt from surfaces, for example, vacuum cleaners, air conditioners and similar devices. Such fans periodically require cleaning but this is not expensive nor too aggravating due to the infrequency of the cleaning.
In the case of a fan operating in an environment where there are very large quantities of extremely sticky substances, the continual requirement to stop and clean-out the fan is both aggravating and expensive in terms of down time.
The "state of the art" potato harvester utilizes a fan which does not work in such an environment. The potato harvester digs up the potatoes, together with rocks, mud, weeds and grasses and conveys most of the mixture to a separator. The separator has a vacuum chamber which includes a system of conveyors and a suction fan. The suction or partial vacuum created inside the vacuum chamber lifts the potatoes which are lighter from a main conveyor onto a potato conveyor permitting the heavier foreign particles, such as rocks to remain on the main conveyor.
It will be apparent that, during operation, in addition to lifting potatoes, there are other sticky substances, such as mud and dirt drawn through the fan housing of the vacuum chamber. If the harvesting conditions are wet, as is quite often the case, then there is a rather rapid build-up of sticky substances on the inner surface of the fan housing. This build-up may become so great as to reduce the effectiveness of the fan to such a degree that the entire potato harvesting machine has to be shut down while the fan housing is cleaned out, usually by manually scraping the build-up from around the inside of the housing.
At the present time, there is a self-cleaning fan housing known in which a strip of conveyor belting is trained around transverse rods so that it is held close to the scroll of the fan housing. While this self-cleaning housing is a great improvement upon housings having no self-cleaning features, it is liable to lose its effectiveness and become inoperative by the build-up of dirt and mud between the conveyor belt and the fan housing. Due to the numerous wear points, there is also a good possibility of the conveyor belt breaking and becoming entangled with the fan so creating extensive damage.